1. Field of the Invention
This invention generally relates to a roller bearing, and, in particular, to a stud type track roller bearing for use in rolling along a guide path of a cam or a straight path of a guide rail.
2. Description of the Prior Art
A stud type track roller bearing is well known in the art and it is also referred to as a cam follower. A stud type roller bearing generally includes a shaft (stud) having a flange at one end, a ring fitted onto the shaft, a plurality of rollers interposed between the shaft and the ring, a retainer for retaining the rollers in position, and a side plate tightly fitted onto the shaft in an opposed relationship with the flange to keep the ring and the rollers in position. In this conventional stud type track roller bearing, when a thrust is produced in the ring because the rollers are skewed, a side wall of the ring is brought into a sliding contact with either the flange or the side plate so that the thrust is absorbed through such a physical contact between the ring and either one of the flange or the side plate. However, if the thrust is relatively large, a significant heat can be produced through such a physical contact, and, as a result, sticking due to burning could result at such a sliding contact. Thus, the bearing could become stuck due to heating in a relatively short period of time under relatively severe conditions, such as the mounting errors are relatively large, the rotating speed is relatively high, and/or the load is relatively large.
In order to cope with the above-described situation, there has been proposed a stud type track roller bearing employing a special thrust washer as disclosed in the Japanese Utility Model Application No. 2-47417 assigned to the assignee of this application. The roller bearing disclosed in this U.M. application is schematically shown in FIGS. 3 and 4 of this application. As shown in FIGS. 3 and 4, this stud type track roller bearing generally includes a ring 11, a shaft or stud 13, a plurality of rollers 12, a retainer 14, a thrust washer 15 and a side plate 16.
The ring 11 has a relatively large thickness and a guide surface 11a is defined along its inner peripheral surface. In addition, a recessed portion 11b having a diameter larger than the inner diameter of the ring 11 is formed on both sides of the ring 11. The shaft 13 is also provided with a guide surface 13a in an opposed relationship with the guide surface 11a of the ring 11. The shaft 13 is, moreover, provided at its one end with a flange 13c having a diameter slightly smaller than the diameter of the recessed portion 11b, so that the flange 13c may be located inside a corresponding recessed portion 11b. The shaft 13 is also provided with a threaded section 13b at the other end for coupling with another element.
When the shaft 13 is fitted into the ring 11, a gap is created between the guide surface 11a of the ring 11 and the opposed guide surface 13a of the shaft 13, and a plurality of rollers 12 are disposed in this gap circumferentially and spaced apart from each other in rolling contact with both of these guide surfaces 11a and 13a. The retainer 14 is also disposed in this gap so as to keep the rollers 12 in position and spaced apart from each other. The side plate 16 having a center hole is tightly fitted onto the shaft 13, for example, through an interference fit and located adjacent to one side of the guide surface 13a in an opposed relationship with the flange 13c. The side plate 16 has an outer diameter which is slightly smaller than the diameter of the recessed portion 11b so that the side plate 16 is also located inside its associated recessed portion 11b when set in position. In the illustrated example, since the guide surface 13a is defined as a peripheral surface of a portion of the shaft 13 which has a larger diameter, the side plate 16 is set in position by bringing in contact with a step of such a larger diameter portion.
The thrust washer 15 is rotatably provided between one side of the ring 11 and the flange 13c and also between the opposite side of the ring 11 and the side plate 16. As shown in FIG. 4, the thrust washer 15 is formed with a plurality of substantially spherically shaped pockets 15a for reserving therein a quantity of lubricant. Thus, the thrust washer 15 is expected to provide a well lubricated contact between the ring 11 and the flange 13c and/or side plate 16, thereby preventing the bearing from becoming stuck due to heating.
However, in the prior art structure, since the contact surface between the ring 11 and the flange 13c or side plate 16 is relatively small so that the load per unit area is relatively large, there is still a danger that the bearing becomes stuck due to excessive heating particularly when the thrust load is relatively large and/or the rotating speed is relatively large. In addition, since the thrust washer 15 is provided with a plurality of substantially circular shaped pockets 15a, the actual contact between the ring 11 and the flange 13c or side plate 16 is reduced, which in turn increases the load per unit area. Moreover, difficulty is encountered in fabricating such a thrust washer 15. Besides, since the gap between the ring 11 and the flange 13c or side plate 16 must be set as small as possible from the viewpoint of preventing any foreign matter from sneaking in, such a condition makes it difficult to manufacture the bearing and thus tends to push up the cost. Finally, since the prior art structure basically relies on the sliding contact using the thrust washer 15, a relatively large torque is required and the thrust washer 15 becomes worn so that the thrust load-bearing characteristic may fluctuate. Thus, the prior art structure is not suited for high speed applications.